This is the VOA Special English Agriculture Report.

American farmers first planted genetically engineered crops in nineteen ninety-six. Today eighty percent of the cropland for soybeans, maize and cotton in the United States is transgenic. Genetic engineering adds or changes genes in a plant to produce desired qualities.

The United States is one of twenty-five countries where farmers planted genetically engineered crops in two thousand nine. An agricultural biotechnology group says planting decreased in Europe. But the amount of cropland planted with the crops rose by an estimated seven percent worldwide.

The National Research Council, part of the National Academies in Washington, recently published a study. The study examined how genetically engineered crops have affected farming in the United States. It found that many farmers have better harvests, better weed control and fewer losses from insect damage compared to traditional crops.

LaReesa Wolfenbarger is a University of Nebraska biology professor and a member of the committee that wrote the report. She says they found that genetically engineered crops can be better for the environment.

LAREESA WOLFENBARGER: "In general, we find that genetically engineered crops have had fewer adverse effects on the environment than non-GE crops produced conventionally."

For example, she noted that crops designed to resist damage by glyphosate need fewer pesticides that are more toxic to the soil. Glyphosate is a chemical used in Round-Up and other weed killing products.

But some farmers have used so much glyphosate that a number of kinds of weeds can now resist it. David Ervin of Portland State University in Oregon led the committee that wrote the report. Professor Ervin says this means that some farmers are again using the more toxic herbicides to control weeds. He says the problem needs immediate attention.

Earlier this year, a professor at the University of Western Australia commented on the overuse of glyphosate. Stephen Powles wrote about it in the Proceedings of the National Academy of Sciences in the United States. He said glyphosate is as important in worldwide food production as penicillin is in medicine for fighting disease. He called for better use of glyphosate-resistant crop technology.

And that's the VOA Special English Agriculture Report, written by Jerilyn Watson, with additional reporting by Steve Baragona. You can comment on our reports at voaspecialenglish.com. You can also get our stories on Facebook, Twitter and YouTube at VOA Learning English. I'm Bob Doughty.